Title of Invention

A METAL / AIR BATTERY OR FUEL CELL AND METHOD OF MAKING THEREOF

Abstract A method of improving the performance of magnesium containing electrodes used in metal/air batteries (fuel cells), comprising the addition of one or more additives are selected from any of the following groups: dithioburet, and tin plus a quaternary ammonium salt
Full Text A METAL / AIR BATTERY OR FUEL CELL AND METHOD OF MAKING
THEREOF
FIELD Of THE INVENTION
The present invention relates to a metal / air battery or fuel cell. Particularly the invention relates to a products and method for improving the performance of magnesium containing metal air battery/fuel cells in one or more ways including: increasing anode utilization efficiency (suppressing hydrogen evolution), increasing energy density, increasing power density or increasing cell voltage.
BACKGROUND
It is well known in the prior art that certain battery electrodes, especially those used in metal-air batteries/fuel cells, suffer from undesirable hydrogen evolution during their "discharge" in which they generate electrical power or when they are stored, due to corrosion and/or moderate energy density i.e. watt-hours/litre output and/or low cell voltage. These electrodes include those containing magnesium and aluminium and/or zinc alone or in combination, as examples. The production of
hydrogen is described by commercial fuel cell (battery) •suppliers (e.g. www. green volt. com/fuel cells . htm) . This producer portrays
this as a safety issue. However it also represents a waste of metal fuel.
It is well documented that magnesium suffers from parasitic hydrogen evolution in inorganic electrolytes. For example Antonyraj (Antonyra j , A. and C. O.. Augustin, 1998, "Anomalous Behaviour of Magnesium Anodes in •Different Electrolytes at High Concentrations", Corrosion Reviews, 16(1-2): 127-138) states "when magnesium metal" comes in contact with aqueous electrolytes, self-dissolution of the metal and the evolution of hydrogen take place simultaneously" (see pg 131). Song et al. (Song, G. et al., 1997, "The Electrochemical Corrosion of Pure Magnesium in IN NaCl", Corrosion Science, 39(5): 855-875) indicate that "under free corrosion conditions, magnesium corrosion can be considered to occur by the interaction of local anodes and cathodes" (see pg 871). 'Song et al. suggest that magnesium can be converted
hydride by the following electrochemical reaction (see pg 858) :
(Formula Removed)
Proof of this suggested mechanism is given by Nazarov et al. (Nazarov, A.P. et al., 1989, "Formation of MgH2 on Electrochemical Dissolution of Magnesium in Aqueous Electrolytes, Zashchita Metallov, 25(5): 760-765).
United States Patent No. 5,024,904, issued to Curiel, describes the use of metal anodes, preferably made of magnesium,•aluminum or magnesium-aluminum alloy, in combination with salt containing electrolytes and air cathodes for purposes of producing portable, direct current electrical power. Testing of the Curiel prototype by the current inventors has revealed the following major
weakness: magnesium utilization efficiency as low as 30% due to parasitic hydrogen, evolution.
United States Patent No. 4,908,281, issued to O'Callaghan describes the undesirable production of hydrogen on aluminum electrodes in aluminum air cells (pg 1 lines 63+). "As with other batteries this hydrogen can easily reach explosive concentrations." (page 2 lines 10 to 12). One of the purposes of the O'Callaghan invention is to create a system designed to properly vent hydrogen to help prevent explosions. The electrolyte is designed to flow upwards and over a weir to discharge aluminum hydroxide product into an electrolyte reservoir. Air is used to dilute hydrogen below explosive limits. Tuck .(Tuck, Clive D.S., Modern Battery Technology, 489-490) also describes parasitic, gaseous hydrogen evolution on. aluminum contained in aqueous electrolytes.
Quraishi et al. (Quraishi, M.A. et al., 1999, "Dithiobiurets: A Novel Class of Acid Corrosion Inhibitors for Mild Steel, Journal of Applied Electrochemistry) have described the inhibition of corrosion/hydrogen evolution
on steel, in strongly acidic environments using 'dithiobiurets with the following structure:
(Structure Removed)
"where R and R' are aryl substituted functional groups such as phenyl,'tolyl and so on.
United States Patent No. 5,004,654 issued to Hunter et al. (corresponding to European patent application EP354752) describes the benefits of a source of tin e.g. tin containing ions such as stannate ions, on undesirable hydrogen evolution in aluminum/air cells.
U.S. Patent No. 4,332,864 issued to King et al. '(corresponding to GB2058837) describes magnesium alloys containing aluminium, zinc and tin used as anode in primary cells with sea water as electrolyte. :
U.S. Patent No. 5,376,471 issued to Hunter et al. (corresponding to European patent application EP0549664) relates to metal/air cells comprising an air cathode and an anode being composed of an aluminium, magnesium, tin' alloy and/or the tin is added in the form of tin dichloride to the electrolyte.
United States Patent No. 3,594,235 issued to Moran describes the use of quaternary ammonium salt containing electrolyte in combination with metal/air batteries (fuel cells) containing cadmium or magnesium electrodes. The use of quaternary ammonium salt as the sole electrolyte component other than water, especially at an .excessively high concentration of 10% by weight, makes the Moran •invention prohibitively expensive for non-military applications.
The prior art related to batteries, especially metal/air batteries (fuel cells) such as those including magnesium and aluminum and/or zinc, alone or in combination e.g. as alloys, has failed to incorporate knowledge in the use of hydrogen evolution inhibitors
derived for steel, especially in highly acidic environments. Attempts to minimize deleterious evolution, of hydrogen have been generally restricted to the use of exotic and/or expensive metal alloys.
Finally, the prior art related to magnesium/air batteries and fuel cells has failed to incorporate knowledge derived by the aluminum industry related to corrosion inhibition by tin containing electrolytes.
Accordingly, it is an object of the current invention to provide improved methods for inhibition of hydrogen evolution (improved anode utilization efficiency) and/or energy density and/or cell voltage and/or power density improvement in batteries, especially metal/air batteries (fuel cells), especially those containing magnesium, magnesium and aluminum, magnesium and zinc.
SUMMARY OF THE INVENTION
The invention relates to a method of improving the performance of magnesium containing electrodes used in
metal/air batteries (fuel cells), comprising the addition of one or more additives to the electrolyte or electrode surface. More specifically it relates to performance improvement due to any one of the following factors alone or in combination: the inhibition of hydrogen evolution (improvement of electrode utilization), improvement of energy density, improvement of power density and/or increase in cell voltage. The additives are selected from any of the following groups: dithiobiuret, -tin,—and tin plus a quaternary ammonium salt.
Advantageously, dithiobiuret additives may be used, which have the following structure:
(Structure Removed)
in which either or both of the R and or R' function groups contain an aryl group (aromatic ring structure), for example, in which R is a tolyl group -C6H5-CH3 and R' is a phenyl group C6H5-.
Tin containing additives may be used either in the electrolyte or on the electrode surface, for example, in the form of stannate salts such as sodium stannate.
Tin containing additives may also be used either in the electrolyte or on the electrode surface, for example, in the form of stannate salts such as sodium stannate, in 'combination with a quaternary ammonium salt such as tricaprylmethylammonium chloride (e.g. Aliquate 336) .
The invention also includes improved metal/air fuel cells and batteries based on the above methods.
DETAILED DESCRIPTION
The following non-limiting examples show the flexibility of the invention as applied to magnesium/air battery/fuel cells:
Example 1
Magnesium AM60 alloy sheet anode (94% magnesium and 6% aluminum content by weight) was submerged together with an air cathode in a seawater electrolyte with and without the addition of 0.0001 molar dithiobiuret containing p-tolyl and phenyl R and R' functional groups, respectively. The cell was operated at a discharge current of 5 amperes
(32 mamp/cm2 starting anode current density) without replenishment of the electrolyte until the cell voltage dropped to zero due to dissolution of magnesium plus aluminum. The electrolyte was initially at room temperature. The average cell voltage, power density
(watts per.liter, W/L) energy density (watt hours per liter, Wh/L) and average anode utilization efficiency
(100% - hydrogen production efficiency) for a single-cell system are summarized below:
(Table Removed)
Example 2
Magnesium AM60 alloy sheet anode was submerged together with an air cathode in a 13% by weight sodium chloride electrolyte with and without the addition of 0.0001 molar dithiobiuret containing p-tolyl and phenyl R and R' functional groups respectively. The cell was operated at a discharge current of 5 amperes (32 mamp/cm2 . starting anode current density) without replenishment of the electrolyte until the cell voltage dropped to zero due to dissolution of magnesium plus aluminum. The electrolyte was initially at room temperature. The
average cell voltage, power density (watts per liter, W/L) energy density (watt hours per liter, Wh/L) and average anode utilization efficiency (100% - hydrogen production efficiency) for a single-cell system are summarized below:

(Table Removed)
Example 3
Magnesium AM60 alloy sheet anode was submerged together with an air cathode in a 24% sodium citrate, 12% sodium sulphate, 1% sodium chloride (all % by weight) electrolyte with and without the addition of .0.003 molar sodium stannate (Na2Sn03) . The cell was operated at a •discharge current of 5 amperes (32 mamp/cm starting anode
current density) without replenishment of the electrolyte until the cell voltage dropped to zero due to dissolution of magnesium plus aluminum. The electrolyte was initially at room temperature. The average cell voltage, power density (watts per liter, W/L) energy density (watt hours per liter, Wh/L) and average anode utilization efficiency (100% - hydrogen production efficiency) for a single-cell system are summarized below:

(Table Removed)
Example 4
The experiment in Example 3 above was repeated with the further addition of a quaternary ammonium salt,
Aliquat 336) to the electrolyte at 0.0001 molar concentration. The average cell voltage, power density (watts per liter), energy density (watt hours per liter, •Wh/L) and average anode utilization efficiency (100% -hydrogen production efficiency) are summarized below:

(Table Removed)
This experiment clearly shows the beneficial interaction between tin and quaternary ammonium salt additives in improvement of the metal/air battery performance with anodes containing magnesium or its alloys.
Example 5
The experiment in Example 4 above was repeated with • the removal of the tin additive (i.e. stannate) from the electrolyte, while retaining the quaternary ammonium salt additive Aliquat 336. The average cell voltage, power density (watts per liter, W/L), energy density (watt hours per liter Wh/L) and average anode utilization efficiency (100% — hydrogen production efficiency) are summarized below:

(Table Removed)
Although the addition of the quaternary ammonium salt _additive improved the cell performance, the combination of tin containing additives with the quaternary ammonium salt
and magnesium containing anodes, was clearly superior to that of a quaternary ammonium salt alone, as shown by the energy density and anode utilization efficiency comparison with Example 4. The combination of a tin additive and a quaternary ammonium salt suppressed hydrogen evolution on a magnesium containing anode to a greater extent than either additive used alone.
Example 6
In order to investigate the effect of the additives in conjunction with zinc-containing magnesium alloys experiments were performed using AZ31 alloy sheet anode submerged with an air cathode in an electrolyte mixture composed of 24% by weight sodium citrate, 12% by weight sodium sulfate and 1% by weight sodium chloride. Experiments were performed with and without additives present in the electrolyte. The additives were either 0.0001 molar Aliquat 336 or a combination of 0.0001 molar Aliquat 336 and 0.003 molar sodium stannate. A discharge current per cell of 5 A was applied (anode current density at start of 35 mamp/cm2) and the experiment was continued until the cell voltage dropped to 0.8 V. The electrolyte
was initially at room temperature and it was used without replenishment. The average cell voltage, power density (watt per liter, W/L), energy density (watt hours per liter, Wh/L) and anode utilization efficiency (100% -hydrogen production efficiency) per single cell are summarized below:

(Table Removed)
The above example shows that using the combination additive (i.e. quaternary ammonium salt Aliquat 336 and stannate) in conjunction with the AZ31 alloy, improved ail 4 performance factors of the magnesium-air fuel cell containing a magnesium-aluminum-zinc alloy.
Accordingly, while this invention has been described with reference to illustrative embodiments, this description is riot intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art

upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments of the invention.






WE CLAIM:
1. A metal / air battery or fuel cell comprising a magnesium-containing
electrode, an air electrode and an electrolyte characterized by:
one or more additives, said one or more additives being added to said magnesium- containing electrode or said electrolyte, said one or more additives being selected from the group consisting of: dithiobiuret, and a tin source plus a quaternary ammonium salt.
2. The metal/ air battery or fuel cell as claimed in claim 1, wherein said tin
source is added to said electrolyte as a stannate salt.
3. The metal/ air battery or fuel cell as claimed in claim 1, wherein said tin
source is added to said electrode surface as tin metal.
4. The metal/ air battery or fuel cell as claimed in claim 3, wherein said stannate
salt is sodium stannate.
5. The metal/ air battery or fuel cell as claimed in claim 1, wherein said
dithiobiuret has the structure:
(Structure Removed)
wherein one or both of the R and R' groups contain an aryl group with an aromatic ring structure.
6. The metal/ air battery or fuel cell of claim 5, wherein said R group is a tolyl
group and said R' group is a phenyl group.
7. A metal / air battery or fuel cell as claimed in claim 1 comprising:
a dithiobiuret additive contacting a surface of said magnesium - containing electrode.
8. A metal / air battery or fuel cell as claimed in claim 7, wherein said
dithiobiuret additive is added to said electrolyte which is in contact with said
magnesium containing electrode.
9. The metal / air battery or fuel cell as claimed in claim 7, wherein said
magnesium- containing electrode is dipped in a dithiobiuret containing
liquid and then allowed to dry.
10. The metal / air battery or fuel cell as claimed in claim 9, wherein said liquid
can evaporate.
11. The metal / air battery or fuel cell as claimed in claim 1, wherein said
quaternary ammonium salt is tricaprylmethyammonium chloride.
12. The metal / air battery or fuel cell as claimed in claim 1, wherein said
magnesium -containing electrode also contains a member selected from the
group consisting of aluminium, tin, zinc and any combination thereof.
13. A metal/ air battery or fuel cell as claimed in claim 1, the method of making
thereof, comprising:
a. Providing a metal/ air battery or fuel cell having an air electrode, an
electrolyte, and a magnesium - containing electrode; and
b. Adding one or more additives to said electrolyte or surface of said
magnesium- containing electrode, said additives selected from the
group consisting of:
dithiobiuret, and a tin source plus a quaternary ammonium salt.
14. The method as claimed in claim 13, wherein said tin source is added to said
electrolyte as a stannate salt.
15. The method as claimed in claim 13, wherein said tin source is added to said
electrode surface as tin metal.
16. The method as claimed in claim 15, wherein said stannate salt is sodium
stannate.
17. The method as claimed in claim 13, wherein said diothiobiuret has the
structure:
(Structure Removed)
wherein one or both of the R and R' groups contain an aryl group with an aromatic ring structure.
18. The method as claimed in claim 17, wherein said R group is a tolyl group and
said R' group is a phenyl group.

Documents:

230-delnp-2004-abstract.pdf

230-delnp-2004-assignment.pdf

230-delnp-2004-claims.pdf

230-delnp-2004-correspondecne-others.pdf

230-delnp-2004-correspondecne-po.pdf

230-delnp-2004-description (complete).pdf

230-delnp-2004-form-1.pdf

230-delnp-2004-form-13.pdf

230-delnp-2004-form-18.pdf

230-delnp-2004-form-2.pdf

230-delnp-2004-form-26.pdf

230-delnp-2004-form-3.pdf

230-delnp-2004-form-5.pdf

230-delnp-2004-pct-101.pdf

230-delnp-2004-pct-102.pdf

230-delnp-2004-pct-105.pdf

230-delnp-2004-pct-106.pdf

230-delnp-2004-pct-132.pdf

230-delnp-2004-pct-135.pdf

230-delnp-2004-pct-202.pdf

230-delnp-2004-pct-210.pdf

230-delnp-2004-pct-220.pdf

230-delnp-2004-pct-301.pdf

230-delnp-2004-pct-304.pdf

230-delnp-2004-pct-308.pdf

230-delnp-2004-pct-332.pdf

230-delnp-2004-pct-401.pdf

230-delnp-2004-pct-402.pdf


Patent Number 218133
Indian Patent Application Number 230/DELNP/2004
PG Journal Number 37/2008
Publication Date 12-Sep-2008
Grant Date 31-Mar-2008
Date of Filing 03-Feb-2004
Name of Patentee MAGPOWER SYSTEMS INC.
Applicant Address SUITE 340-6165 HIGHWAY 17, DELTA, BRITISH COLUMBIA, CANADA V4K 5B8.
Inventors:
# Inventor's Name Inventor's Address
1 KLAUS HEINRICH OEHR 1940-180TH STREET SURREY, BRITISHA COLUMBIA V3S 9V2 CANADA.
2 STEVEN SPLINTER 1830 BURRIL AVENUE, NORTH VANCOUVER, BRITISH COLUMBIA V7K 1M2 CANADA
3 ELOD LAJOS GYENGE 307-1827 WEST 3RD STREET, VANCOUVER, BRITISH COLUMBIA V6K 1K9 CANADA
4 JOEY CHUNG- YEN JUNG 972-51ST STREET, DELTA, BRITISH COLUMBIA V6N 2R5, CANADA
5 COLIN WILLIAM OLOMAN 3176 WEST 36TH AVENUE VANCOUVER, BRITISH COLUMBIA V6N 2R5, CANADA
PCT International Classification Number H01M 12/06
PCT International Application Number PCT/CA02/00976
PCT International Filing date 2002-06-25
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 09/919,599 2001-08-01 U.S.A.